A Bis(hexadentate) Biphenyl‐Based N 12 Ligand and Its Fe II Complexes

The novel biphenyl‐based ligand N , N′ , N″ , N″′ ‐tetrakis(2,2′‐bipyridin‐6‐ylmethyl)‐4,4′‐dimethyl‐1,1′‐biphenyl‐2,2′,6,6′‐tetramine ( 6 ) with 12 nitrogen donor atoms has been synthesized. Ligand 6 is able to host two metal ions in an octahedral coordination sphere. This was shown by the synthesis of the dinuclear iron(II) complex 5 ([Fe 2 ( 6 )] 4+ ). Furthermore, the corresponding mononuclear iron(II) complex 4 ([Fe( 6 )] 2+ ), where one coordination site is free, was obtained. Both Fe II complexes show spin‐crossover behaviour, which was shown by 1 H NMR spectroscopy and Evans' measurements. A comparison of the two complexes gives evidence of a sterically induced cooperative behaviour in the dinuclear complex 5 .